Thermal ink jet (TIJ) print heads produce ink droplets from thermal vaporization of the ink solvent. In the jetting process, a resistor is heated rapidly to produce a vapor bubble which subsequently ejects a droplet from the orifice. This process is extremely efficient and reproducible. Modern TIJ print heads for industrial graphics applications are capable of generating uniform drops of 4 pL or smaller in volume at frequencies of 36 kHz or greater. Typical commercial TIJ devices are specifically designed to vaporize water or solvents that have physical properties close to those of water (e.g. high boiling point, large heat capacity, low molecular weight).
Although TIJ printing systems have been available for over 30 years, most of the commercial inks available for thermal ink jet systems have been water-based, i.e. they contain more than 50% water. Such aqueous inks have one or more drawbacks such as long ink dry times or poor adhesion to semi-porous or non-porous substrates. Since around 2009 an increasing number of solvent-based TIJ inks have been proposed or introduced, with varying degrees of success. These formulas have performance and shelf-life limitations due to material incompatibility with traditional thermal ink jet cartridges.
There is a desire for inks with attractive performance characteristics such as short dry times, long decap times and good adhesion when using a TIJ system to print onto semi-porous and non-porous substrates.